The specific objectives of this project are to obtain data which can be used to provide a molecular explanation of the control and mechanism of the membrane-membrane interactions which cause the aggregation of human blood platelets. The scientific background of this proposal is the demonstrated role of membrane lectins in mediating direct cell-cell interaction of metazoan cells, e.g. facilitating fusion of myoblasts. Ferritin labeling studies, platelet membrane binding studies, platelet aggregation studies, use of platelets as affinity adsorbents for purification of lectin molecules and receptors are the methods and procedures that will be used in this project. The potential clinical significance of this work is that it will provide insight into the molecular basis of the malfunction of certain types of defective platelets, e.g. Glanzmann's Thrombasthenia and it may also result in the purification or synthesis of compounds whch can be used to control or prevent the formation of platelet caused thrombi.